JP2617118B2 - Rare earth permanent magnet with excellent corrosion resistance and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a permanent magnet alloy containing R, Fe, and B as a main component, and particularly to a rare earth permanent magnet alloy having excellent corrosion resistance and improved magnet properties, and its use. It relates to a manufacturing method.

[Prior Art] Generally, an R-Fe-B-based permanent magnet alloy is obtained by crushing an ingot having a predetermined structure and sintering it by a powder metallurgy method. It has higher magnetic properties than Sm-Co based magnets, which are conventional rare earth magnets.

However, since the R-Fe-B-based magnet alloy contains an Nd-Fe solid solution phase which is very easily oxidized in this metal composition, when incorporated into a device such as a magnetic circuit, the Rm-Fe-B-based magnet alloy has an Sm even under ordinary environmental conditions. -Deterioration of characteristics due to oxidation of the magnet and its variation are larger than those of the Co-based magnet. Further, scattering of the oxide generated from the magnet also affects the peripheral portion.

For this reason, an attempt to improve the corrosion resistance by plating the obtained magnet is disclosed in JP-A-49-86896 or JP-A-49-86896.
Although it is proposed in Japanese Patent Application Laid-Open No. 0-63901, it is difficult to prevent oxidation generated during the manufacture of the magnet in this case.

Conventionally, when electrolytic plating is performed in a water-soluble plating bath, plating can be performed on the surface of the base Nd-Fe-B magnet, but the adhesion between the plating film and the base is insufficient, and blistering occurs.
Defects such as exfoliation often occur, there is a problem that rust occurs during use from the Nd-Fe solid solution phase which is extremely easily oxidized in the metal structure, and it is not possible to obtain a plating film having excellent corrosion resistance. I have.

Also, in the case of the present magnetic alloy, when the processed product is small or thin (eg, 3 mm or less in thickness), a phenomenon occurs in which the magnet characteristics are significantly deteriorated.

This is because the R ₂ Fe ₁₄ B phase on the processed magnet surface is not wrapped in the Nd-rich phase which is indispensable for generating coercive force, so that the exposed R ₂ Fe ₁₄ It is considered that the magnetization of the B phase occurs due to reversal at a low magnetic field. That is, since the coercive force is significantly reduced in the magnet surface layer, if the magnet product is small or thin, the reduced coercive force on the magnet surface or the characteristics of the entire magnet body is significantly affected, and the demagnetization curve is reduced. It is reported that the square shape and the like are deteriorated (Japanese Patent Application Laid-Open No. 61-281850).

As a countermeasure, there has been reported a method of coating R or Fe alloy on the surface of processed R / Fe / B magnet by sputtering or vapor deposition, or recovering the coercive force of the surface by applying heat treatment. ing. (Japanese Unexamined Patent Publication No. 61
-281850, JP-A-62-192566).

[Problems to be Solved by the Invention] However, these methods such as sputtering have a problem that the mass productivity is extremely low and the cost is high.

Further, even if the coercive force of the surface is restored by this sputtering method, the surface of the magnet contains R, which is extremely active in the atmosphere, as a main component. Therefore, it is necessary to coat an oxidation-resistant film thereon.

As described above, since the magnet surface is an extremely active layer in the atmosphere containing R as a main component, it is difficult to handle such an oxidation-resistant film. Since the magnet surface is oxidized during the process, the coating film is peeled off, the corrosion resistance is deteriorated, and the magnet characteristics are further deteriorated. That is, it is not suitable as a measure for improving the magnet properties and the corrosion resistance.

Therefore, the present invention is to solve the above-mentioned drawbacks, and the technical problem is that, by performing electrolytic plating in a plating solution to which R ions or Fe ions have been added in advance, R, Fe element is contained, plating film with concentration distribution of R and Fe is formed between the surface and inside of the plating film, good adhesion to the substrate and excellent corrosion resistance, and by heat treatment after plating In particular, it is an object of the present invention to provide a rare earth permanent magnet alloy having improved coercive force with small articles, thin articles, and the like, and a method for producing the same.

[Means for Solving the Problems] According to the present invention, in a rare earth magnet having a metal coating on the surface of an R—Fe—B (where R is a rare earth element containing Y) magnet alloy, the metal coating is formed by electrodeposition. A rare earth permanent magnet excellent in corrosion resistance is obtained, including the formed electrolytic plating film made of a metal imparting corrosion resistance, wherein the electrolytic plating film contains R or Fe.

According to the present invention, an R-Fe-B (where R is a rare earth element containing Y) -based surface is electroplated with an electrolytic plating film for imparting corrosion resistance from an alkaline bath or an acidic bath. In the method for producing a magnet, the alkaline bath or the acidic bath contains at least one R ion or Fe ion.
A method for producing a rare-earth permanent magnet excellent in corrosion resistance characterized by containing a seed is obtained.

Here, in the present invention, it is desirable that at least one of the R ions or Fe ions has a concentration in the range of 0.01 mol / to 1.0 mol /.

Here, in the method for producing a rare earth permanent magnet excellent in corrosion resistance of the present invention, after electrodeposition of the electrolytic plating film, 400
It is desirable to perform a heat treatment at a temperature of from 1 ° C to 1100 ° C.

Normally, when electrolytic plating is performed in an aqueous plating bath in which a metal salt is dissolved, the adhesion between the Nd—Fe—B magnet alloy as a base and the plating film is not very good. In this case, defects such as blister peeling often occur and are extremely oxidized in the metal structure.
Rust is generated during use from the Nd-Fe solid solution phase, and oxidation proceeds from that portion even under normal environmental conditions.

Thus, the poor adhesion between the substrate and the plating film is a major problem. Normally, the surface condition, pretreatment step, plating conditions, and the like are examined in order to improve the adhesion, but the effect is not sufficient. In addition, the deterioration of magnet properties when processed into small or thin objects is also a major problem. Therefore, in the present invention, if the plating solution used contains R ions or Fe ions in advance, not only metal ions for plating but also R and Fe ions in the solution precipitate on the cathode during electrolytic plating, and Contained in the membrane. At this time,
Since the R and Fe ions in the plating solution are consumed and not supplied from the anode side, the ion concentration of the solution decreases. As a result, it becomes possible to form a plating film having a concentration distribution in which the R and Fe elements gradually decrease from the magnet surface toward the plating layer surface, and this plating film has very good adhesion to the substrate, Therefore, the effect of Fe ion addition was remarkable.

The metal used for the electrolytic plating of the aqueous solution containing R and Fe ions may be any metal that is less oxidizable than the rare earth metal contained in the magnet.
A Watt bath for Ni plating, a copper sulfate bath for Cu plating, and a sulfuric acid bath for Sn plating are conceivable. On the other hand, examples of the alkaline electrolytic plating bath include a copper pyrophosphate plating bath for Cu plating and a sodium bath or potassium bath for Sn plating.

The amount of R ions or Fe ions contained in these aqueous electrolytic plating baths is desirably in the range of 0.01 mol / to 1 mol /, and below 0.01 mol /, the amount of R and Fe elements contained in the plating film is small. Therefore, the above effects cannot be obtained. 1 mol
In the case of / or more, since Nd is contained in the plating layer in a large amount, the corrosion resistance of the plating layer itself is deteriorated, so that the range of 0.01 to 10 mol / is desirable.

If the thickness of the plating film is 0.1 (μm) or less, plating is not sufficiently performed, so oxidation on the magnet surface proceeds, and
Above (μm), the non-magnetic portion contained per unit volume of the magnet increases and the magnetic performance of the magnet deteriorates. Therefore, the thickness of the plating film is preferably in the range of 0.1 to 10 (μm).

When performing electrolytic plating, usually, after immersing a sample in a plating solution, voltage is applied to perform electrolytic plating.
However, immersing the Nd-Fe-B magnet specimen in the plating bath,
If left as it is, the Nd-Fe solid solution phase will melt and corrode. Therefore, if a voltage is applied from the beginning to a predetermined current density while immersing in a plating solution and performing electrolytic plating, a clean plating film having good adhesion is formed.

Further, when a heat treatment is performed after plating in the present invention, the adhesion between the magnet surface and the plating film can be improved, and the magnet properties can be improved. This is because the heat treatment causes diffusion of atoms. The heat treatment temperature is desirably in the range of 400 ° C. to 1100 ° C. If the temperature is lower than 400 ° C., diffusion does not sufficiently occur, and if the temperature is 1100 ° C. or more, grain growth in the sintered body occurs and magnet characteristics are deteriorated.

According to the present invention, a plating film having good adhesion and excellent corrosion resistance is formed on the magnet surface by performing electrolytic plating using a plating bath containing R ions or Fe ions in advance. Further heat treatment makes it possible to obtain a practically useful magnet with improved magnetic properties.

 Hereinafter, embodiments of the present invention will be described.

[Example] Example 1 33 wt% Nd-1.0 wt% BF obtained by powder metallurgy
A sintered body having a composition of e bal was processed into a size of 1 × 7 × 10 (mm) to obtain a sample. To a copper pyrophosphate plating bath (strike bath) shown in Table 1, a 0.1 mol / Nd ion / Fe ion solution was added.

Cu plates to the anode side, and Nd-Fe-B sintered samples were placed in the cathode side, at a current density of 1.0A / dm ² at a bath temperature of 25 ° C. 30 minutes Cu
Plating was performed.

Under the above conditions, a Cu plating film with a thickness of about 10 μm
-Plated on the Fe-B magnet surface. At this time, the adhesion between the substrate and the Cu plating was very good, and a Cu plating film with good adhesion was obtained.

The cross section inside this plating film is EDX (energy dispersive X
Composition analysis using a line analyzer). Table 2 shows the results.

The plating film near the surface of the Nd-Fe-B magnet has more Nd and Fe than others, and the plating film has a concentration distribution of Nd and Fe.

Table 3 shows the results of qualitatively confirming the effects of applying an external force (friction, bending, impact, etc.) to the specimen as an adhesion test.

Next, the plated sample was subjected to a heat treatment under the conditions of 400 to 1000 ° C. × 0.5 hr. Table 4 shows the results of the magnetic properties ( _I H _C ) at that time.

Improvement of the magnetic properties _(I H _C) was observed in the heat treatment condition of 500 ° C. to 800 ° C. × 0.5 hr, in particular, when the 600 ℃ × 0.5Hr _I H _C
12.0 (kOe) was obtained.

Further, the surface of the Nd-Fe-B magnet was subjected to electrolytic Ni plating after Cu underplating. Table 5 shows the results obtained when these test pieces were subjected to a corrosion resistance test for 1500 hours under the conditions of constant temperature and humidity of 60 ° C. × 95% humidity.

The test piece according to the present invention was found to be extremely excellent in corrosion resistance without causing defects such as red rust, peeling and blistering.

Example 2 0.1 mol in a watt bath (nickel plating bath) shown in Table 6.
/ Nd ion and Fe ion solutions were added.

As a Ni plate on the anode side and a Nd-Fe-B sintered body test on the cathode side, Ni plating was performed at a current density of 4.0 A / dm ² for 10 minutes at a bath temperature of 50 ° C. Ni with a thickness of about 10μm under the above conditions
The plating film was plated on the Nd-Fe-B magnet surface.

The adhesion between the substrate and the Ni plating was very good, and no defects such as blistering and peeling were observed in the adhesion test.

The cross section inside this plating film was subjected to composition analysis by EDX. Table 7 shows the results.

The plating film near the surface of the Nd-Fe-B magnet contained more Nd and Fe than the others, and the Nd and Fe concentration distribution was found in the plating film.

Next, the plated sample was subjected to a heat treatment at 600 ° C. × 0.5 hr. As a result _I H _C was improved from 8 (kOe) to 11.5 (kOe).

Further, when a corrosion resistance test was conducted for 1500 hours under a constant temperature and humidity condition of 60 ° C. × 95% humidity, no change such as red rust, blistering and peeling was observed.

[Effects of the Invention] As described above, in the rare earth permanent magnet having corrosion resistance and the method of manufacturing the same according to the present invention, the surface of the magnet is prepared by performing aqueous electrolytic plating using a plating bath containing R ions or Fe ions in advance. A plating film containing R and Fe elements in the plating film and having a concentration distribution of R and Fe between the inside and the surface of the plating film is formed. This plating film has a good adhesion to the substrate and a magnet having excellent corrosion resistance can be obtained. Further, by performing a heat treatment after plating, it is possible to recover the magnet properties, and it is possible to promote the improvement of the coercive force particularly for small and thin objects.

Claims (2)

(57) [Claims] A rare earth permanent magnet having a metal coating on the surface of an R-Fe-B (R is a rare earth element containing Y) magnet alloy, wherein the metal coating is made of a metal imparted with corrosion resistance formed by electrodeposition. Including an electrolytic plating film, wherein the electrolytic plating film is R
Or a rare earth permanent magnet excellent in corrosion resistance characterized by containing Fe. 2. An electrolytic plating film is electrodeposited on an R-Fe-B (where R is a rare earth element containing Y) magnet alloy surface from an alkaline bath or an acidic bath to impart corrosion resistance. In the method for producing a magnet, the alkaline bath or the acidic bath contains at least one kind of R ion or Fe ion, and the method for producing a rare earth permanent magnet excellent in corrosion resistance is provided.